Rotor end turn ventilation structure

Abstract: An improved rotor end winding assembly for an electrodynamic apparatus includes a stack (16) of conductive straps that are configured to turn about an end turn portion of a rotor and include a top strap (18), a bottom strap (20) and a number of intermediate straps (46) that are stacked between the top strap (18) and the bottom strap (20). A space defined between the rotor shaft and the bottom strap (20) is divided into a high pressure zone (32) and a low pressure zone (34) by a zone block (36). A stepped coolant passage (40) defined in the stack includes an ascending passage (42) that leads from the high pressure zone (32) toward the top strap and in the direction of the zone block (36) and low pressure zone (34), and a descending passage (48) that leads from the ascending passage (42) to the low pressure zone (34). As a result, coolant will flow from the high pressure zone (32) to said low pressure zone (34) to efficiently cool said stack (16) of straps (46).

Description: This invention relates to the design of large electrodynamic equipment, such as electrical generators. More specifically, this invention relates to an improved cooling system for the end turn region of a strap-wound rotor coil in an air-cooled electrical generator. Economic concerns dictate that large, air-cooled electrical generators of the tyupe that are manufactured by the assignee of this invention, Westinghouse Electric Company, be designed to as high a power density as possible, as well as being simple to manufacture. The higher the power density of an electrical generator, the more heat that is produced in the stator and rotor windings during normal operation. The need to conduct waste heat away from the stator and rotor windings thus operates as a significant constraint to the power density that can be achieved. Traditionally, the end turn region of strap-wound rotor windings have been difficult to effectively cool. One method of cooling the end turns involves machining ventilation channels into fiberglass blocking that is located between the coil end turns, thus conducting heat away from the side surfaces of the coils. However, the effectiveness of such ventilation channels is limited, and is inadequate to provide the cooling that would be necessary at the level of power densities that the designers of such equipment are trying to achieve. Cooling arrangements for generator rotors are known. An improved cooling arrangement for the winding of a dynamoelectric machine rotor is disclosed in U.S. Patent No. 2,986,664 issued May 30, 1961 in the name of David M. Willyoung, et al. This patent discloses an arrangement employing an improved "direct-cooled" conductor strand suitable for producing diagonal flow of the coolant within the rotor winding slots with a special arrangement for cooling the rotor body end portions. More specifically, the Willyoung, et al. Device provides a winding utilizing conductor strands of generally rectangular cross-section with a double row of elongated slots punched in the strand along the slot portion of the conductor. Each row of slots in each strand is lightly offset from the row of slots in the adjacent strands above and below so that the slots define a number of diagonal flow passages for the coolant. Additionally, according to the Willyoung, et al. patent, the row of slots on one side of the conductor strand is displaced with respect to the other row of slots so that one row "moves" with respect to the other row from one strand to the next. In this manner, the diagonal coolant passages on one side of the strand will slant in an opposite direction from those on the other side of the strand. Thus, when a number of strands are super-imposed, a series of "criss-crossed" diagonal cooling passages is furnished which transport the coolant longitudinally as well as radially through all of the conductor layers. It is clear that there is a long and unfilled need in the prior art for an improved method and system for cooling the end turn regions of strap-wound rotor coils in an electrical generator. SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide an improved system for cooling the end turn region of strap-wound rotor coils in an electrical generator. In order to achieve the above and other objects of the invention there is provided a rotor end winding assembly for an electrodynamic apparatus such as an electrical generator comprising: a rotor shaft; a stack of a plurality of conductive straps, said stack of straps having an end turn portion, said stack of straps including a top strap, a bottom strap and a number of intermediate straps that are stacked between said top and bottom strap, characterized by: a space defined between said rotor shaft and said bottom strap, said space being divided into a high pressure zone and a low pressure zone by a zone block; a coolant passage defined in said stack, said coolant passage comprising: an inlet hole defined in said bottom strap adjacent to said high pressure zone; a number of ascending holes defined, respectively, in a number of said intermediate straps to define an ascending passage that leads toward said top strap and in the direction of said zone block and low pressure zone; an outlet hole defined in said bottom strap adjacent to said low pressure zone; and a number of descending holes that define a descending passage which is in communication with said ascending passage at a first end and with said outlet hole at a second end; whereby coolant will flow from said high pressure zone to said low pressure zone to efficiently cool said stack of straps. These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. FIGURE 1 is a fragmentary perspective view of an electrical generator assembly that is constructed according to a preferred embodiment of the invention, partly in schematic, and with parts broken away for clarity; FIGURE 2 is a fragmentary cross-sectional view of a portion of the generator assembly that is depicted in FIGURE 1; and FIGURE 3 is a cross-sectional view taken along lines 3-3 in FIGURE 2. Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views and referring first to FIGURE 1, an electrical generator assembly 10 that is constructed according to a preferred embodiment of the invention includes a stator assembly 12 and a rotor assembly 14 that is mounted for rotation within the stator assembly 12. The end turn portion of the winding on rotor assembly 14 is depicted in FIGURE 1, and includes a number of stacks 16 of conductive straps. Each stack 16 of straps includes a top strap 18, a bottom strap 20 and a number of intermediate straps 46, which are best shown in FIGURE 2 and 3. Depending on the winding pattern that is being utilized, adjacent straps might not be in electrical contact. Adjacent straps may be in physical contact, or there might be a slight gap and/or insulation material therebetween. For purposes of this document, such adjacent straps are considered to be "in contact." It should be understood that top strap 18 and bottom strap 20 refer generally to the topmost and bottommost straps, respectively, and that the topmost and bottommost straps, as a result of the winding pattern, might not physically be the same strap throughout an entire end turn. Blocking 22, preferably fiberglass, is provided between the stacks 16 of straps to provide structural support during rotation of the shaft 24 of the rotor assembly 14. As is common in such systems, a sliplayer is provided over the top-most straps 18 of the respective stacks 16, and a retaining ring 26 is fitted over the stacks 16, and the sliplayer to provide structural containment of the end turn assembly of rotor 14 during the high speed rotation that occurs during normal operation. Generator assembly 10 is of the air-cooled variety. Referring briefly to FIGURE 3, it will be seen that a number of ventilation passages 28 are defined in the fiberglass blocking 22 that is interposed between adjacent stacks 16 of conductive straps. Ventilation passages 28 are the primary conduits through which coolant flows to provide cooling to the end turn portion of rotor assembly 14. However, the cooling capacity of such passages are insufficient to permit the high power density that the designers of generator assembly 10 intend to facilitate. Accordingly, one important aspect of the invention is the provision of a supplemental ventilation structure 30 that is provided within the stacks 16 of straps themselves. Looking now to FIGURES 2 and 3, it will be seen that a space 38 is defined between the bottom strap 20 of strap stack 16 and the outer circumferential surface of rotor shaft 24. As may be seen in FIGURE 2, a zone block 36 is interposed between rotor shaft 24 and bottom strap 20 within the space 38. Zone block 36 separates space 38 into a high pressure zone 32 and a low pressure zone 34. In the preferred embodiment, the respective pressures in zones 32, 34 result from the application of a positive pressure of coolant into the high pressure zone 32. As is shown in FIGURE 2, a number of stepped coolant passages 40 are defined within the stack 16 of straps to communicate the high pressure zone 32 with the low pressure zone 34. As may be seen in FIGURE 2, stepped coolant passage 40 includes an inlet hole 44 that is defined in bottom strap 20 adjacent to the high pressure zone 32, a number of overlapping, ascending holes 52 that are defined, respectively, in a number of the intermediate straps 46 to define an ascending passage 42 that leads toward the top strap 18 and in the direction of the zone block 36 and low pressure zone 34. Stepped coolant passage 40 further includes an outlet hole 50 that is defined in bottom strap 20 adjacent to the low pressure zone 34. A descending passage 48 is in communication with the ascending passage 42 at a first end, and with the outlet hole 50 at a second, opposite end. Descending passage 48 is defined by a number of overlapping descending holes 54 that are defined in a corresponding member of the intermediate straps 46. As may further be seen in FIGURE 2, both the ascending holes 52 and descending holes 54 are constructed and arranged so that a first hole in a first strap is in communication with a second hole in a second adjacent strap, and so that the first and second holes are displaced from each other so that a portion of the first strap overlays the second hole, and a portion of the second strap overlays the first hole. As a result of this "staircase" or stepped configuration, the stepped passage 40 has a larger surface area exposed for heat transfer between a coolant and the strap stack 16 than a non-stepped passage would have. It is to be understood, however, that modifications are possible within the scope of the appended claims.

Claims: An improved rotor end winding assembly for an electrodynamic apparatus such as an electrical generator (10), comprising: a rotor shaft (24); a stack (16) of a plurality of conductive straps (46), said stack of straps having an end turn portion, said stack of straps including a top strap (18), a bottom strap (20) and a number of intermediate straps that are stacked between said top and bottom strap, characterized by: a space (38) defined between said rotor shaft and said bottom strap, said space being divided into a high pressure zone (32) and a low pressure zone (34) by a zone block(36); a coolant passage (40) defined in said stack, said coolant passage comprising: an inlet hole defined in said bottom strap adjacent to said high pressure zone; a number of ascending holes (52) defined, respectively, in a number of said intermediate straps to define an ascending passage (42) that leads toward said top strap and in the direction of said zone block and low pressure zone; an outlet hole (50) defined in said bottom strap adjacent to said low pressure zone; and a number of descending holes (54) that define a descending passage (48) which is in communication with said ascending passage at a first end and with said outlet hole at a second end; whereby coolant will flow from said high pressure zone to said low pressure zone to efficiently cool said stack of straps. An assembly according to claim 1, wherein said descending holes are constructed and arranged so that a first hole in a first strap is in communication with a second hole in a second strap, and so that said first and second holes are displaced from each other so that a portion of said first strap overlays said second hole, and a portion of said second strap overlays said first hole, whereby said descending passage has a larger surface area exposed for heat transfer with a coolant than a non-stepped passage would have. An assembly according to claim 1, wherein said ascending holes are constructed and arranged so that a first hole in a first strap is in communication with a second hole in a second strap, and so that said first and second holes are displaced from each other so that a portion of said first strap overlays said second hole, and a portion of said second strap overlays said first hole, whereby said ascending passage has a larger surface area exposed for heat transfer with a coolant than a non-stepped passage would have. An assembly according to claim 1, wherein said top strap (18) has no hole defined therein that is in communication with said passage. An assembly according to claim 1, wherein said ascending holes (52) each have substantially the same size and shape. An assembly according to claim 1, wherein said descending holes (54) each have substantially the same size and shape.

Inventors: BISELI KATHLEEN M, MONTGOMERY LON W, SISMOUR ALBERT C JR, WELBORN CLIFF A, BISELI, KATHLEEN M., MONTGOMERY, LON W., SISMOUR, ALBERT C., JR., WELBORN, CLIFF A.
Applicants: WESTINGHOUSE ELECTRIC CORP, WESTINGHOUSE ELECTRIC CORPORATION
Application year: 1994
Main classification: H02K3
IPC codes: H02K3